Sexual Reproduction in Flowering Plants

The tip region of the ovule where the micropyle is located.

The basal region of the ovule opposite the micropylar end.

The process of forming female gametophyte (embryo sac) in the ovule.

The single cell in the nucellus that undergoes meiosis to form four megaspores.

The transfer of pollen grains from the anther to the stigma.

Transfer of pollen grains from the anther to the stigma of the same flower.

Transfer of pollen grains from the anther of one flower to the stigma of another flower on the same plant.

Self-pollination that occurs in closed, unopened flowers.

A cross-section of the anther reveals a four-sided structure, with four microsporangia located within each lobe. These microsporangia eventually develop into pollen sacs, which extend the length of the anther.

The outer layers of the microsporangium, including the epidermis, endothecium, and middle layers, provide protection and facilitate the release of pollen grains. The innermost layer, called the tapetum, provides nourishment for developing pollen grains.

The sporogenous tissue within the young microsporangium is composed of cells that will function as microspore mother cells. These cells undergo meiosis to produce four haploid microspores.

The process of meiosis in a microspore mother cell, resulting in the formation of four haploid microspores, is known as microsporogenesis.

The four microspores produced from a microspore mother cell often arrange themselves in a tetrad called a microspore tetrad.

Freshly formed microspores contain abundant cytoplasm and a centrally positioned nucleus. As the microspore matures, the nucleus shifts to the periphery, a large central vacuole develops, and the microspore wall differentiates.

The microspore divides mitotically, leading to two daughter cells: a smaller generative cell and a larger vegetative cell. This is the stage at which pollen grains are typically shed in 60% of angiosperms.

Pollen grains are generally spherical and consist of two distinct wall layers. The outer layer is called the exine, and the inner layer is called the intine.

Transfer of pollen from anther to stigma of another flower on a different plant of the same species.

A mode of pollination where pollen is transferred by wind.

Anemophilous flowers are usually small, colorless, odorless, and lack nectar. They have large stigmas to catch airborne pollen.

A mode of pollination where pollen is transferred by insects.

Entomophilous flowers are typically large, brightly colored, and produce specific scents to attract insects.

A mode of pollination where pollen is transferred by water.

Hydrophilous flowers are adapted to avoid getting wet. They have long, sticky stigmas.

A relationship where a species provides a safe place for another species to lay eggs in exchange for pollination.

The point where the funicle (stalk) attaching the ovule to the placenta joins the body of the ovule.

The protective layers surrounding the ovule. They develop from the parent sporophyte and are diploid (2n).

The innermost layer of the ovule, surrounding the embryo sac and containing the female gametophyte.

The female gametophyte, containing the egg cell and other cells, within the ovule.

The state of an embryo entering a period of inactivity during seed maturation, allowing for survival during unfavorable conditions.

A type of reproduction without fertilization, where a plant develops an embryo directly from the ovary wall or other tissues.

A type of flower that opens fully, exposing its reproductive parts to allow for cross-pollination.

A type of flower that remains closed, resulting in self-pollination.

A protective sheath covering the root tip of monocot embryos.

The persistent nucellus (remnant of the megasporangium) in black pepper seeds.

The process of removing anthers from a flower to prevent self-pollination.

The technique of covering emasculated flowers with a bag to prevent unwanted pollination.

A structure at the micropylar end of the synergid cells in the embryo sac, guiding pollen tube growth.

The outer layer of a maize grain, derived from the ovary wall.

The fusion of a male gamete with the egg cell to form a zygote.

The fusion of a male gamete with the two polar nuclei in the central cell to form the primary endosperm nucleus.

The organic material, sporopollenin, makes up the exine of the pollen grain. It's incredibly resistant to degradation by harsh environments, ensuring the pollen's survival during dispersal. It's even found in ancient fossils!

The pollen bank serves as a repository for storing diverse pollen grains, preserving genetic diversity for future use. It's crucial for research, breeding programs, and conservation efforts.

Farmers use the dormancy of seeds to their advantage by storing them for extended periods. They can be planted when conditions are ideal for germination, ensuring a successful crop.

Parthenocarpy is the development of fruit without fertilization, often resulting in seedless fruit, while apomixis is the production of seeds without fertilization, where the embryo arises from the maternal tissues.

Farmers prefer using apomictic seeds as they produce genetically identical offspring, ensuring desirable traits are passed on. This eliminates the hassle of cross-pollination and guarantees consistent plant characteristics.

Syngamy, the fusion of male and female gametes, is crucial for sexual reproduction, as it leads to genetic diversity and the formation of a zygote. Meiosis, on the other hand, is essential for reducing the chromosome number, ensuring that each gamete receives half the number of chromosomes from the parent cell.

Monoecious plants have both male and female flowers on the same plant, while diecious plants have separate male and female plants. For example, maize is monoecious, while papaya is diecious.